Image URLs in social previews are not prefixed with backend URL

[soudis]

In the SocialPreview (FacebookPreview and TwitterPreview) the image urls are not prefixed with the backend URL.

In our setup we have the fronted at a specific URL (example.com) and the backend / strapi sitting at a subpath (example.com/strapi). Other strapi plugins or the content manager can handle this because they use the prefixFileUrlWithBackendUrl helper function when dealing with image urls. The seo plugin however just uses the plain url and therefore the images are not shown in the preview.

I created a (not yet tested) PR: #36

[hovcharenko]

I'd like to vote on this one too, we're experiencing the same issue under same conditions